#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
 
int main()
{
	int n;
	cin>>n;
	vector<int> a(n);
	for(int i = 0; i < n; ++i){
		cin>>a[i];
	}
	sort(a.begin(), a.end());
	int ans = 0; 
	for(int i = 0; i < n; ++i){
		++ans;
		int cur = i;
		for(int j = i+1; j < n && a[j] <= a[cur] + 4; ++j){
			++i;
		}
	}
	cout<<ans;
	// your code goes here
	return 0;
}